Preparation of 157nm transmitting barium fluoride crystals with permeable graphite

摘要

The present invention is directed to a method of making large diameter metal fluoride sungle crystals that can be used in optical lithograpby systems, for example, excimer laser that operate below 200 nm. In addition, the invention is directed to metal fluoride single crystals suitable for use in such lithographic ststems, such fluoride crystals having a internal transmission of ≧99.9% at 193 nm and ≧99.0% at 157 nm.